System of modulation



Aug. 20, 1929. J PARKER 1,724,960

SYS TEM OF MODULAT I ON Filed March 1, 1923 Wi l gwuentoz James E. Parker Patented Aug. 20, 1929.

UNITED STATES JAMES E. PARKER, OF WASHINGTON, DISTRICT OF COLUMBIA.

SYSTEM OF MODULATION.

Application filed March 1, 1923. Serial No. 622,002.

My invention relates to a system of modulation and an object thereof is to provide a system of this character which is more simple and eflicient in operation than similar systems now known.

It is well known that in a vacuum tube or )ther form of sensitive gap oscillatory circuit having sustained oscillations it is required to re-enforce the variations of the current in the supply circuit to maintain oscillations in the system. The mutual reactions of the currents in the oscillatory circuit and the supply circuit may be so arranged as to tend to build up the oscillations in the oscillatory circuit until a maximum has been reached.

This maximum will remain at a fixed value as long as the characteristics of the circuit and tube remain unchanged. It is also well known that where a mutual reactance between the oscillatory circuit and the supply circuit is arranged variation in the amplitude of the oscillations will be magnified through such mutual reaction or feedback effect.

The purpose of the present invention is to cause high percent variation or modulation in the amplitude of the oscillations in the oscillatory circuit, in response to feeble oscillations applied to said circuit.

\Vith the above and other objects in view I will now describe in detail my system as applied to a simple oscillatory circuit, it being understood, of course, that the particular oscillatory circuit shown in the figure is for illustrative purposes only, and that my system of modulation is equally well adapted to any conventional oscillatory circuit.

Reference is to be had to the accompanying drawings, in which: 7

The figure is a diagrammatic view of my modulation system combined with a typical oscillatory circuit.

The oscillatory system includes the condenser C, and if desired, antenna A, and ground G72, inductance coils L and L,, the usual plate battery PB and the vacuum tube T by which the oscillations are generated. Such a system is well known, and a description of its operation is thought to be unnecessary. 7

The modulating circuit consists of a vacuum tube T having the plate thereof adjustabl connected to the oscillatory system as by tile connection B to coil L,; the circuit comprising plate P inductance L and filament F Connected with the grid G, and filament F of the tube T is the microphone circuit, including transformer M and microphone transmitter N. It will be understood that any type of interrupter may be substituted for the microphone transmitter.

In view of the mutual reaction of coils L and L in the building up and maintaining of oscillations in the oscillatory system, it is evident that plate P of the modulating tube T may be adjustably connected to inductance coil L instead of L or to other well known methods of operatively associating two circuits, and still be within the spirit of the invention.

In operation, the potential on grid G is varied by the potential changes in the secondary of the transformer, which potential changes are caused by the action of the interrupter or the voice waves on the microphone transmitter. This variation of the grid potential varies the resistance of the path between the filament F and the plate P of the tube T and hence varies the strength of the current flowing in the modulation circuit, the correct variation being obtained by controlling the potential impressed. on the plate-filament circuit of the tube T by the oscillating circuit as obtained through the variable connect-ion B of the two circuits. It will be noted that no other platefilament potential is employed in the case of the tube T If the resistance of the path between the filament and plate of tube T is so great as to entirely block the current flow in the modulation circuit when the oscillating potential on the plate P is correct, the oscillating system will function normally. If the resistance of the path is reduced, there will be a flow of current in the modulating circuit with the result that the output of the oscillating system will be reduced, and this effect can be properly controlled through the adjustable connection B.

From the foregoing it will be clear that my system directly controls the strength or amplitude of the oscillations in any type of sustained wave oscillatory system, and that the control is accomplished by resistance variations properly coordinated with the magnitude of the oscillations, which variations are in turn controlled b a microphone transmitter, interrupter, or t e like.

Obviously my system can be employed in radio telephony, radio telegraphy, or in any case Where it is desirable to use a vacuum tube to control by resistance variations the output of any oscillatory system.

Having fully described my invention, what I desire to secure by Letters Patent is:

1. In a radio transmitter including a vacuum tube oscillator with plate-filament and grid-filament circuits coupled to an antenna, the combination of a second vacuum tube having a filament, grid, and plate, means for va"ying the electrical potential of the gridthereof, and means for supplying potential to the plate thereof, said means consisting of a step-down autotransformer in the grid-filament circuit of the oscillator tube.

2. In a radio transmitter including a vacuum tube oscillator with plate-filament and grid-filament circuits, coupled to an antenna, the combination of a second vacuum tube having a filament, grid, and plate, means for varying the electrical potential of the grid thereof, and means for supplying potential to the plate thereof, said means consisting of a step-down autotransformer in the grid filament circuit of the vacuum tube oscillator, said autotransformer having a variable ratio of transformation.

3. In combination with a vacuum tube oscillator, a coil, an intermediate point of which is connected to the filament of said oscillator, one extremity of said coil connected to the grid of said vacuum tube cs cillator to form the grid-filament circuit thereof, the other extremity of said coil connected to the plate of said vacuum tube oscillator to form the plate-filament circuit thereof, and means connected to said coil for modulating the alternating current generated by said oscillator, said means comprising a second vacuum tube, having grid-filament circuitand plate filament circuits, said grid filament circuit havingcoupled thereto a modulator, and said plate filament circuit including a portion of said coil intermediate its extremities. V

4. In combination with a vacuum tube oscillator, a, coil, an intermediate point at Which is connected to the filament of said oscillator, one extremity of said coil connected to the grid of said vacuum tube oscillator to form the grid-filament circuit thereof, the other extremity of said coil connected to the plate of said vacuum tube oscillator to form the plate-filament circuit thereof, and means connected to said coil for modulating the alternating current generated by said oscillator, said means comprising a second vacuum tube, having a gridfilament and plate-filament circuits, a transformer the secondary of which is included in the grid-filament circuit of said second vacuum tube, the filament of said second vacuum tube connected to the intermediate point on said coil and the plate of said second vacuum tube variably connected to said coil at points intermediate its extremities, to form a step-down autotransformer along said coil in the plate-filament and grid-filament circuits of said vacuum tube oscillator.

JAMES E. ARKER. 

